Crack repair using friction stir welding on materials including metal matrix composites, ferrous alloys, non-ferrous alloys, and superalloys

Abstract

A system and method of using friction stir welding and friction stir processing to perform crack repair or preventative maintenance of various materials and structures, wherein the structures include pipeline, ships, and nuclear reactor containment vessels, wherein the friction stir welding and processing can be performed on various materials including metal matrix composites, ferrous alloys, non-ferrous alloys, and superalloys, and wherein the friction stir welding and processing can be performed remotely and in harsh environments such as underwater or in the presence of radiation.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This document incorporates by reference all of the subject matter filed in U.S. patent Ser. No. 6,648,206, in U.S. patent application Ser. No. 09 / 851,597 (now allowed), and in U.S. patent application Ser. No. 10 / 846,825.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates generally to friction stir welding wherein heat for creating a weld is generated by plunging a rotating pin of a tool into a workpiece. More specifically, the present invention relates to performing crack repair, crack prevention, and material conditioning in a friction stir welding process that enables the present invention to repair or perform pre-emptive maintenance on materials that are welded, wherein the present invention is particularly applicable to the repair and maintenance of pipes, and has important applicability to the nuclear energy industry. [0004] 2. Description of Related Art [0005] Crack formation and propagation ...

AI Technical Summary

Benefits of technology

[0013] It is another object to provide a system and method that enables preventing crack initiation and propagation by using friction stir welding.

[0015] It is another object to provide a system and method that enables repair and prevention of cracks in harsh environments, including underwater and nuclear environments.

[0018] It is another object to provide a system and method for friction stir welding that utilizes a run-off tab to avoid holes in the subject material being modified or repaired.

Problems solved by technology

Crack formation and propagation is a serious problem in many applications that use metal and alloy structures and components.

It is well known in the industry that crack initiation can be a result of loading, hydrogen embrittlement, corrosion, stress corrosion, material defects, and especially fusion welding defects.

In particular, the process of fusion welding introduces residual stresses caused by solidification of a liquid phase, solidification cracking, porosity, large grain sizes prone to grain boundary corrosion, and crack initiation sites that originate from the heat affected zone.

While a need has been established to friction stir weld high melting temperature alloys for improved properties (making it possible to achieve 95%+ base metal properties), a methodology has not yet been established to repair cracks, except in aluminum alloys.

For example, fusion welding is not a viable process for repairing welds in fluid or underwater environments.

Fusion welding is even difficult to perform in air environments because of the cast structure that is created from a molten phase, and the accompanying defects.

Failure of pipes or other structures that are subject to the effects of crack propagation is a problem with serious consequences not only for the environment, but the health of workers.

Leaks in such an environment can have serious health consequences for those involved.

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